Absorption vacuum dehumidification system and method using the same

ABSTRACT

An absorption vacuum dehumidification system includes a vacuum section, an absorber, a desorber, a photovoltaic energy supply, a heat exchanger, a condenser, and a desiccant solution. The vacuum section has a feed side and a permeate side and comprising a hydrophilic membrane that separates the feed side than the permeate side. The absorber is connected to the permeate side of the vacuum section. The desorber is connected to the absorber to form a desiccant solution cycle path between the absorber and the desorber. The photovoltaic energy supply configured to power a heat source that provides hot liquid into the desorber. The heat exchanger is connected to the desiccant solution cycle path. The condenser is connected to the desorber. The desiccant solution flows along the desiccant solution cycle path.

CROSS-REFERENCES WITH RELATED APPLICATIONS

The present application claims priority from a U.S. provisional patentapplication Ser. No. 63/340,475 filed on 11 May 2022, and the disclosureof which are incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an absorption vacuum dehumidificationsystem, and more particularly, to an absorption vacuum dehumidificationsystem that integrates an absorption refrigeration cycle into the systemand a method using the same.

BACKGROUND

As the major electricity consumers in buildings, the energy performanceof air-conditioning systems is always one of the main areas of research.In particular, the precise indoor temperature and humidity control isnot an easy task, especially in tropical/sub-tropical regions. Thesituation is getting even more challenging in view of the threat fromCOVID-19 which necessitates the use of more fresh air for indoorventilation.

The need for fresh air supply inevitably leads to a rise in energydemand and thus carbon emissions for ventilation, especially in tropicaland sub-tropical regions. For regions with heavy moisture, an effectivedehumidification mechanism is one of the needed solutions formaintaining air quality. The common use of cooling and reheating coilsto achieve independent temperature and humidity may not be effectiveunder a high latent load ratio. The employment of dedicateddehumidification systems in parallel with conventional air-conditioningequipment can be a better choice.

In particular, the shift to a heat-driven approach in which solar energyor waste heat from a trigeneration system is utilized as the drivingpower, can further escalate the sustainability of the dehumidificationsystem in terms of reduction in carbon emissions.

Currently, the most common dehumidification systems employ solid orliquid desiccant dehumidification cycles. Both are thermally-drivenwhich can use solar or waste heat, resulting in substantial reduction inelectricity demand and hence carbon emissions. However, solid desiccantdehumidification systems are usually bulkier and may not be suitable ina densely-populated city.

Liquid desiccant dehumidifiers comparatively require less space.Nevertheless, one concern of using liquid desiccant dehumidifiers is thecarryover of liquid desiccant to the air stream. As liquid desiccant isusually corrosive, this can lead to serious problems. Studies have beenmade to solve problem. FIG. 1 shows a mechanism of membranedehumidification system using liquid desiccant according to a prior art.One consideration is to separate the liquid desiccant 10 and 12 and airstream 14 and 16 by a selective (such as hydrophilic) membrane 18. Watervapor 20 is then transferred from the moist air to the liquid desiccantthrough the membrane 18.

Zhai et al. [1] reviewed the techniques of applying membrane fordehumidification or cooling using liquid desiccant. The membrane may befabricated in a tubular form with the liquid desiccant running insidethe tube while the air passes through the outside of the tube [2-7]. Itmay also be flat sheets sandwiched between the liquid desiccant streamand the air stream [8-11]. In all cases, the liquid desiccant is indirect contact with the membrane. Hence, the requirement for themembrane material becomes more stringent due to the corrosive propertyof the liquid desiccant. Moreover, the dehumidification process isexothermic as phase change occurs when the moisture is transferred fromthe air side to the liquid desiccant side. This is not desirable as theair will be heated up unless the liquid desiccant is pre-cooled orinter-cooling is provided.

To relieve such problem, vacuum dehumidification (VD) is regarded as apotential alternative. In vacuum dehumidification, water vapor from amoist air stream is directly extracted away through a selective membraneto a low-pressure or vacuum section. The water vapor does not undergo aphase change and the process can be considered to be isothermal. FIG. 2shows a schematic diagram of a conventional vacuum dehumidificationsystem driven by an electrical vacuum pump according to a prior art.With moist air 30 fed into a “feed side 32” adjacent to a hydrophilicmembrane 34, water vapor or permeate 36 is transferred to the “permeateside 38” through the membrane 34 under a water vapor pressure differenceon both sides of the membrane 34. The permeate 36 is then extracted bythe vacuum pump 40 driven by the electricity supply 42 to the ambient44, and the dehumidified air 32 leaves as a retentate. As thisdehumidification process is isothermal, the energy performance of the VDsystem is better.

The concept of vacuum dehumidification by using electrical vacuum pumpis not new with a few patents which can be dated back to 1988 [12-19].Qu et al. [20] thoroughly reviewed the research works of membranedehumidification including vacuum dehumidification. Other studies onvacuum dehumidification [21-30] also only considered the use ofelectrical vacuum pump to develop the vacuum condition. In this regard,the energy efficiency of the vacuum pump is critical to the overallenergy performance of the VD systems as remarked by Bui et al. [28].This could be challenging for a small-capacity system which led theresulting system coefficient of performance (COP) not better than thatof an absorption chiller. In other words, the primary energy consumptionand consequently the carbon emissions could be even higher than those ofan absorption chiller which is not favorable.

Besides the use of electrical vacuum pumps, there can be other ways togenerate the vacuum condition, such as a thermally-driven mechanism. Inthis situation, solar or waste heat can be utilized which enhances thesustainability of the dehumidification systems. Recently, Fong and Lee[31] proposed a heat-driven vacuum dehumidification system whichintegrated the VD into the evaporator of an adsorption refrigerationcycle. As remarked by Fong et al. [32], an absorption chiller (AbC) ismore energy efficient than an adsorption chiller if the temperature ofthe heat source is sufficiently high.

As outlined above, the current state of the art in dehumidification ischaracterized by a number of significant obstacles. To overcome thesechallenges, there is a critical need for innovative approaches that cancreate a more practical and energy-efficient system.

SUMMARY OF INVENTION

To address the problem as above, a novel heat-driven absorption vacuumdehumidifier (AbVD) is proposed, which integrates a vacuum dehumidifierinto an absorption refrigeration cycle. This system achievesdehumidification of a moist air stream solely through a hydrophilicmembrane inside a vacuum section, while maintaining the temperature ofthe air stream.

In accordance with a first aspect of the present invention, anabsorption vacuum dehumidification system is provided, including avacuum section, an absorber, a heat exchanger, a desorber, andcondenser. The absorber is connected to a permeate side of the vacuumsection, in which cooling water is input in and output from theabsorber. Hot water is input to and output from the desorber. The heatexchanger is connected between the absorber and the desorber. Coolingwater is input in and output from the condenser. A weak desiccantsolution is pumped to the desorber and is heated up at the desorber.First water vapor is desorbed from the weak desiccant solution and istransferred to the condenser. The transferred first water vapor iscooled to become liquid water at the condenser. A strong desiccantsolution leaving the desorber is pre-cooled at the heat exchanger beforeentering the absorber. The strong desiccant solution is diluted byabsorbing second water vapor which is extracted from a moist air streamentering a feed side of the vacuum section through the hydrophilicmembrane, and a dehumidified air stream is outputted from the vacuumsection.

In accordance with a second aspect of the present invention, a methodfor an absorption vacuum dehumidification system is provided, includingsteps as follows: pumping a weak desiccant solution to a desorber,wherein the weak desiccant solution is heated up at the desorber by hotwater inputted into the desorber such that first water vapor is desorbedfrom the weak desiccant solution and is then transferred to a condenser;inputting cooling water to the condenser, such that the transferredfirst water vapor is cooled down to become liquid water at thecondenser; transferring a strong desiccant solution from the desorber toan absorber, wherein a heat exchanger is instructed to pre-cool thestrong desiccant solution before the strong desiccant solution entersthe absorber; and extracting second water vapor from a moist air streamwhich enters a feed side of a vacuum section through a hydrophilicmembrane, so as to output a dehumidified air stream from the vacuumsection, wherein the strong desiccant solution is diluted by absorbingthe second water vapor inside the absorber.

In accordance with a third aspect of the present invention, anabsorption vacuum dehumidification system is provided, including avacuum section, an absorber, a desorber, a photovoltaic energy supply, aheat exchanger, a condenser, and a desiccant solution. The vacuumsection has a feed side and a permeate side and comprising a hydrophilicmembrane that separates the feed side than the permeate side. Theabsorber is connected to the permeate side of the vacuum section. Thedesorber is connected to the absorber to form a desiccant solution cyclepath between the absorber and the desorber. The photovoltaic energysupply configured to power a heat source that provides hot liquid intothe desorber. The heat exchanger is connected to the desiccant solutioncycle path. The condenser is connected to the desorber. The desiccantsolution flows along the desiccant solution cycle path.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention are described in more details hereinafterwith reference to the drawings, in which:

FIG. 1 shows a mechanism of membrane dehumidification system usingliquid desiccant according to a prior art;

FIG. 2 shows a schematic diagram of a conventional vacuumdehumidification system driven by an electrical vacuum pump according toa prior art;

FIG. 3 shows a schematic diagram of an absorption vacuumdehumidification system according to some embodiments of the presentinvention;

FIG. 4 shows variation of cooling capacities of an absorption vacuumdehumidifier with cooling water supply temperature under different hotwater supply temperatures;

FIG. 5 shows variation of coefficient of performance of an absorptionvacuum dehumidifier with cooling water supply temperature underdifferent hot water supply temperatures;

FIG. 6 shows variation of thermal power inputs of an absorption vacuumdehumidifier with cooling water supply temperature under different hotwater supply temperatures;

FIG. 7 shows variation of a performance improvement index of coefficientof performance with cooling water supply temperature under different hotwater supply temperatures;

FIG. 8 shows variation of a performance improvement index of coefficientof performance with cooling water supply temperature under different hotwater supply temperatures; and

FIG. 9 shows variation of cooling capacities and coefficient ofperformance of an absorption vacuum dehumidifier with feed air supplytemperatures.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, an absorption vacuum dehumidificationsystem and a method using the same and the likes are set forth aspreferred examples. It will be apparent to those skilled in the art thatmodifications, including additions and/or substitutions may be madewithout departing from the scope and spirit of the invention. Specificdetails may be omitted so as not to obscure the invention; however, thedisclosure is written to enable one skilled in the art to practice theteachings herein without undue experimentation.

FIG. 3 shows a schematic diagram of an absorption vacuumdehumidification system 100 according to some embodiments of the presentinvention. The absorption vacuum dehumidification system 100 of thepresent invention can be referred to as an absorption vacuumdehumidifier as well. The absorption vacuum dehumidification system 100includes a vacuum section 102, an absorber 110, a desorber 112, a heatexchanger 114, a condenser 116, a desiccant pump 118, and an expansionvalve 120.

The vacuum section 102 includes a chamber in accordance with someembodiments. The vacuum section 102 can be referred to as a vacuumchamber, dehumidification chamber, or membrane dehumidification chamber.The vacuum section 102 has a feed side 104 and a permeate side 106 andincludes a hydrophilic membrane 108 that separates the feed side 104than the permeate side 106.

The absorber 110 is connected to the permeate side 106 of the vacuumsection 102. In some embodiments, the absorption vacuum dehumidificationsystem 100 further includes a vapor tube 122 connecting the vacuumsection 102 to the absorber 110. In some embodiments, the vapor tube 122is configured to deliver water vapor from vacuum section 102 to theabsorber 110. During a dehumidification operation, the absorber 110serves as a part of a desiccant solution cycle path, as the hydrophilicmembrane 108 can be physically separated from a desiccant solution ofthe desiccant solution cycle path, such the configuration excludes thedirect contact of the hydrophilic membrane with the corrosive desiccantsolution, which can relieve the anti-corrosive requirement of thehydrophilic membrane and broaden the choice of the hydrophilic membranematerials for performance advancement. The absorber 110 can be connectedto an external cooling water supply, so cooling water is input to andoutput from the absorber (i.e., cooling water in/out).

The desorber 112 is connected to the absorber 110 to form a desiccantsolution cycle path between the absorber 110 and the desorber 112.Herein, the desiccant solution cycle path means a desiccant solution canflow from the absorber 110 to the desorber 112 and then flow back fromthe desorber 112 to the absorber 110. The desorber 112 can be connectedto a heat source 130, so hot water is input to and output from thedesorber 112 (i.e., hot water in/out). For example, the absorptionvacuum dehumidification system 100 further includes an energy supplyconfigured to power the heat source 130 that is connected to thedesorber 112 and provides hot liquid into the desorber 112.

The heat exchanger 114 is connected between the absorber 110 and thedesorber 112 and thus is connected to the desiccant solution cycle path.The desiccant pump 118 is disposed between the absorber 110 and the heatexchanger 114 so thus is in communication with the desiccant solutioncycle path. The expansion valve 120 is disposed between the absorber 110and the heat exchanger 114 so thus is in communication with thedesiccant solution cycle path. As such, the desiccant solution cyclepath includes a first desiccant solution path P1 and a second desiccantsolution P2. The first desiccant solution path P1 is from the absorber110 to the desorber 112 at least through the desiccant pump 118 and theheat exchanger 114. The second desiccant solution path P2 is from thedesorber 112 to the absorber 110 at least through the heat exchanger 114and the expansion valve 120.

The condenser 116 is connected to the desorber 112 and is configured toreceive water vapor form the desorber 112. The absorber 110 can beconnected to an external cooling water supply, so cooling water is inputin and output from the condenser 116 (i.e., cooling water in/out). Thecondenser 116 may further include an outlet configured to flow liquidwater out from the condenser 116.

In the following, the absorption vacuum dehumidification operation isdescribed as starting from the absorber 110, which is shown forexplanation purposes only but the invention is not so limited as otherconfigurations may also be used.

A desiccant solution can flow within the desiccant solution cycle path.In some embodiments, the desiccant solution includes lithium bromide.For example, a weak desiccant solution inside the absorber 110 is pumpedto the desorber 112 along the first desiccant solution path P1 by thedesiccant pump 118. At the desorber 112, the weak desiccant solution isheated by hot water input to the desorber 112 such that water vapor isdesorbed from the weak desiccant solution and is then transferred to thecondenser 116. At the condenser 116, cooling water is input to thecondenser 116, so the transferred water vapor is cooled down to becomeliquid water which can be collected for other purpose. In someembodiments, the air pressure inside the condenser 116 is equal to theair pressure inside the desorber 112.

After desorbing the water vapor from the weak desiccant solution, it istransformed into a strong desiccant solution which is then transferredfrom the desorber 112 to the absorber 110 along the second desiccantsolution path P2. Herein, the terms “weak desiccant solution” and“strong desiccant solution” are relative to each other with respect toconcentration thereof; for example, the weak desiccant solution has aconcentration of 0.06 weaker than that of the strong desiccant solution.In some embodiments, the concentration includes a concentration oflithium bromide. In some embodiments, the weak desiccant solution mayhave a concentration of 0.56, and the strong desiccant solution may havea concentration of 0.62. During the transfer of the strong desiccantsolution, the heat exchanger 114 (such as a desiccant-to-desiccant heatexchanger) is instructed to pre-cool the strong desiccant solutionleaving the desorber 112 before the strong desiccant solution enters theabsorber 110. Once pre-cooled, the strong desiccant solution flowingfrom the heat exchanger 114 is throttled by the expansion valve 120 andthen fed into the absorber 110.

At the absorber 110, the strong desiccant solution is diluted byabsorbing water vapor. This process is facilitated by supplying coolingwater to the absorber 110 to lower the temperature and maintain a lowpressure condition inside the absorber 110. As the cooling water entersand exits the absorber 110, it cools down the strong desiccant solutioninside the absorber 110, allowing water vapor to be absorbed by thecooled strong desiccant solution. This results in a lower concentrationof the desiccant solution, which can be referred to as a weak desiccantsolution and then be recycled back to the desorber 112 to complete thecycle. The low pressure maintained in the absorber 110 also results fromthe absorption of the water vapor into the strong desiccant solution.

Regarding the water vapor inside the absorber 110, it flows from thevacuum section 102 via the vapor tube 122. As a moist air stream A1enters the feed side 104 of the vacuum section 102, water vapor 109 canbe extracted from there through the hydrophilic membrane 108 in whichthe extraction involves permeation. More specifically, driven by a watervapor pressure difference on both sides of the hydrophilic membrane 108,the water vapor 109 can be extracted directly from the moist air streamA1 to the permeate side 106 with lower pressure through the hydrophilicmembrane 108. Therefore, the moist air stream A1 can become dehumidifiedand is to be output from the vacuum section 102, so what leaves thevacuum section 102 is a dehumidified air stream A2. The extracted watervapor 109 flows from the vacuum section to the absorber 110 and is to beabsorbed by the strong desiccant solution. In some embodiments, the airpressure inside the absorber 110 is equal to the air pressure inside thepermeate side 106 of the vacuum section 102.

By the above configuration, absorption vacuum dehumidification iscompleted with the desiccant solution cycle path. Since the feed side104 of the vacuum section 102 is physically separated from the desiccantsolution cycle path at least by the vapor tube 122 and the permeate side106, the feed side 104 can provide a flowing path to allow the moist airstream A1 to flow through the feed side 104 without involving with thedesiccant solution cycle path. As such, the dehumidification process tothe air stream (i.e., the moist air stream A1 and the dehumidified airstream A2) is maintained isothermal and does not heat up the air stream,which can achieve higher cooling capacity accordingly.

the above mechanism or effect can be verified through the followingcontent and diagrams. To investigate the performance of the absorptionvacuum dehumidifier (AbVD), a mathematical model is derived forcomparison with the conventional absorption chiller (AbC).

The formulations for the respective physical properties are based onthose presented by Patek and Klomfar [33]. For the refrigerant (water),the corresponding state properties are evaluated according to theequations adopted by Florides et al. [34].

The heat input and cooling capacity of the AbVD could be calculatedfrom:

Q _(heat) =M _(hw) c _(p,w)(T _(hw,o) −T _(hw,i))  (1)

Q _(vs) =m _(da)(h _(a,i) −h _(a,o))  (2)

For the absorption chiller (AbC), the respective cooling capacity wasthen:

Q _(evap) =M _(ew) C _(p,w)(T _(ew,i) −T _(ew,o))  (3)

The COP of the AbC and AbVD was given by:

$\begin{matrix}{{COP}_{AbC} = \frac{Q_{evap}}{Q_{heat}}} & (4)\end{matrix}$ $\begin{matrix}{{COP}_{AbVD} = \frac{Q_{vc}}{Q_{heat}}} & (5)\end{matrix}$

To compare the performance between the AbC and the AbVD, a performanceimprovement index (PII) in term of the cooling capacity (CAP) and COPwas defined so that:

$\begin{matrix}{{PII}_{CAP} = {\frac{Q_{vs}}{Q_{evap}} - 1}} & (6)\end{matrix}$ $\begin{matrix}{{PII}_{COP} = {\frac{COP_{AbVD}}{COP_{AbC}} - 1}} & (7)\end{matrix}$

To compare the performance between the AbVD and the conventional AbC,the parameter values from Heroid et al. [35] is adopted for the AbC andsimilar components in the AbVD. Regarding the vacuum section of theAbVD, respective parameter values from Bukshaisha and Fronk [26] isselected for the membrane which corresponded to a water permeance ofapproximately 2.38×10⁻⁶ kmol/s m² kPa.

The feed air flow rate is taken as 0.62 m³/s at an entering condition of33° C. db and 67% RH. The selected air flow rate and total membrane areaare based on the criterion that the resulting desorber and absorberpressures of the AbVD will be similar to those of the AbC. Then,respective parametric studies are conducted to evaluate the performancesof the AbVD under different operating conditions.

Performance of the AbVD at Default Conditions

TABLE 1 Summarized performances of the AbVD. Parameter Value P_(des)7.213 P_(abs) 0.666 T_(hw, o) 96.53 T_(abw, o) 37.52 T_(cw, o) 34.50Q_(heat) 14.523 Q_(vc) 11.658 COP 0.803 PII_(CAP) 0.097 PII_(COP) 0.103

Table 1 summarizes the performances of the AbVD system under the defaultoperating conditions. It could be found that the performances of theAbVD are better than those of the AbC in terms of both cooling capacityand COP with improvement measured around 10%. This is beneficialparticularly when the primary energy consumption is considered. In fact,by comparing the AbVD with a conventional chilled water air-conditioningsystem, there is no need to have evaporator coil in the chiller andcooling coil in the air-handling equipment. Hence, a better energyperformance will result.

Sensitivity Analysis of the AbVD Performances Under Different OperatingConditions

Referring to FIG. 4 and FIG. 5 , the variation of the system coolingcapacities and COP's of the AbVD with the cooling water supplytemperature under different hot water supply temperatures areillustrated. The trends for the cooling capacities as indicated in FIG.4 are close to those of a conventional absorption chiller in which thecooling capacity decreased with an increase in the cooling water supplytemperature or decrease in hot water supply temperature.

However, the trends for the COP's shown in FIG. 5 appear to be differentfrom those of an absorption chiller in which the COP should reach amaximum at some hot water supply temperatures as indicated in [35]although the fluctuation range is only mild based on the span of hotwater supply temperatures investigated. Instead for the AbVD, the COPdecreases monotonically with an increase in hot water supplytemperatures over the range of cooling water supply temperaturesconsidered.

To explain such a different observation, it should be reminded thatunlike the AbC, the refrigerant side of the AbVD is basically an opencircuit. The condenser pressure plays no role on the cooling capacity ofthe AbVD. It is only the evaporator pressure that could affect thecooling capacity. To further account for these results, FIG. 6 shows thevariation of the thermal power input with the cooling water supplytemperature at different hot water supply temperatures for the AbVD.

Referring to FIG. 6 , the patterns look normal as compared to those ofthe AbC. However, it can be found that the rates of change of thethermal power input with the hot water supply temperature are higherthan those of the cooling capacity. Consequently, the COP decreased withan increase in hot water supply temperature. From FIG. 5 and FIG. 6 , acompromise should be made between the cooling capacity and COP whenselecting the optimal hot water supply temperature.

FIGS. 7 and 8 show the corresponding variation of PII_(COP) andPII_(CAP) under different combinations of the hot and cooling watersupply temperatures. Both PII's increased substantially with an increasein cooling water temperature and/or a decrease in hot water temperature.This is particularly attractive for a solar cooling system in which thesystem capacity and COP of the AbVD does not deteriorate so much ascompared to that of AbC when the solar energy is not sufficient. Indeed,with a hot temperature of 70° C. and a cooling water temperature ofabove 25° C., the capacity and COP of the AbC already become zero.Meanwhile, the AbVD can still function under such circumstances whichfacilitated its operation in a solar cooling system.

FIG. 9 depicts the variation of the system performances of the AbVD withthe feed air temperature. In this analysis, the same humidity ratio asthat of the default air condition is employed. It can be found that theimpact of the feed air temperature on the AbVD performance is limited.This is contrary to the case with the employment of the AbC plus acooling coil as the cooling capacity would decrease with a reduction inthe feed air temperature under such circumstance. Based on FIG. 9 , itcan be expected that PII_(CAP) should increase with a decrease in supplyair temperature.

Based on above, it is found that the AbVD offered around 10% improvementin the system cooling capacity and COP respectively under the designconditions. The COP of the AbVD is even better than that based on theelectrical vacuum dehumidifiers of similar cooling capacity whichhighlights the merit of the proposed AbVD over the electrical vacuumdehumidifiers in view of the primary energy consumption. Parametricstudies on the performances of the AbVD under different combinations ofthe hot water and cooling water supply temperatures are made. It isfound that the trends for the cooling capacity variation are similar tothose of the AbC. However, the situation is different for the variationof COP with the hot water and cooling water supply temperatures. Unlikethose for the AbC in which the COP should reach a maximum as some hotwater supply temperature, the COP of the AbVD decreases strictly with anincrease in the hot water supply temperature over a range of coolingwater supply temperatures considered. This can be accounted for by thefact that the rate of increase in the heating power input is greaterthan the cooling capacity when the hot water temperature increases.

Nevertheless, the choice of the optimal hot water supply temperaturerequires a compromise between cooling capacity and COP which isdifferent from that for the AbC. The PII' s of the AbVD improved at ahigher cooling water temperature and a lower hot water temperature whichdeems the AbVD much more suitable for use in a solar cooling system withunstable heat energy input. Accordingly, the AbVD can have much betterprospect than the electrical vacuum dehumidifier, particularly in small-to medium-capacity applications for the development of sustainableair-conditioning systems. In some embodiments, the AbVD can have theutilization of thermal energy such as solar or waste heat for driving aheat source. In some embodiments, as shown in FIG. 3 , the energy supplyelectrically connected to the heat source 130 is photovoltaic module orcell (e.g., solar module or cell).

The foregoing description of the present invention has been provided forthe purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed.Many modifications and variations will be apparent to the practitionerskilled in the art.

The embodiments are chosen and described in order to best explain theprinciples of the invention and its practical application, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with various modifications that are suited tothe particular use contemplated.

NOMENCLATURE

-   -   CAP cooling capacity (kW)    -   COP coefficient of performance    -   c_(p) specific heat capacity at constant pressure (kJ/kg K)    -   h specific enthalpy (kJ/kg)    -   m mass flow rate (kg/s)    -   PII performance improvement index    -   Q thermal power (kW)    -   T temperature (° C.)

SUBSCRIPT

-   -   a air    -   AbC absorption chiller    -   AbVD absorption vacuum dehumidifier    -   CAP capacity    -   COP coefficient of performance    -   da dry air    -   evap evaporator    -   ew chilled waterheat heating    -   hw hot water    -   i inlet    -   outlet    -   vs vacuum section    -   w water

ABBREVIATIONS

-   -   AbC absorption chiller    -   AbVD adsorption vacuum dehumidifier    -   db dry-bulb temperature    -   RH relative humidity    -   VD vacuum membrane dehumidification

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1. An absorption vacuum dehumidification system, comprising: a vacuumsection; an absorber connected to a permeate side of the vacuum section,wherein cooling water is input in and output from the absorber; adesorber, wherein hot water is input in and output from the desorber; aheat exchanger connected between the absorber and the desorber; and acondenser, wherein cooling water is input in and output from thecondenser, wherein a weak desiccant solution is pumped to the desorberand is heated up at the desorber, wherein first water vapor is desorbedfrom the weak desiccant solution and is transferred to the condenser,wherein the transferred first water vapor is cooled down to becomeliquid water at the condenser, wherein a strong desiccant solutionleaving the desorber is pre-cooled at the heat exchanger before enteringthe absorber, and the strong desiccant solution is diluted by absorbingsecond water vapor which is extracted from a moist air stream entering afeed side of the vacuum section through the hydrophilic membrane, and adehumidified air stream is outputted from the vacuum section.
 2. Theabsorption vacuum dehumidification system of claim 1, furthercomprising: a desiccant pump disposed between the absorber and the heatexchanger; and an expansion valve disposed between the absorber and theheat exchanger, wherein the weak desiccant solution is pumped to thedesorber by the desiccant pump, wherein the strong desiccant solutionpre-cooled by the heat exchanger is throttled by the expansion valve andfed into the absorber.
 3. The absorption vacuum dehumidification systemof claim 1, wherein the cooling water input in and output from theabsorber is configured to facilitate absorption of the second watervapor inside the absorber into the strong desiccant solution and todilute the strong desiccant solution, wherein the absorption of secondwater vapor makes the absorber maintained at a low pressure.
 4. Theabsorption vacuum dehumidification system of claim 1, wherein pressureinside the condenser is equal to pressure inside the desorber, andpressure inside the absorber is equal to pressure inside the permeateside of the vacuum section.
 5. The absorption vacuum dehumidificationsystem of claim 1, wherein at least one of the weak desiccant solutionand the strong desiccant solution comprises lithium bromide.
 6. A methodfor absorption vacuum dehumidification, comprising: pumping a weakdesiccant solution to a desorber, wherein the weak desiccant solution isheated up at the desorber by hot water input into the desorber such thatfirst water vapor is desorbed from the weak desiccant solution and isthen transferred to a condenser; inputting cooling water to thecondenser, such that the transferred first water vapor is cooled down tobecome liquid water at the condenser; transferring a strong desiccantsolution from the desorber to an absorber, wherein a heat exchanger isinstructed to pre-cool the strong desiccant solution before the strongdesiccant solution enters the absorber; and extracting second watervapor from a moist air stream which enters a feed side of a vacuumsection through a hydrophilic membrane, so as to output a dehumidifiedair stream from the vacuum section, wherein the strong desiccantsolution is diluted by absorbing the second water vapor inside theabsorber.
 7. The method of claim 6, further comprising: pumping the weakdesiccant solution to the desorber by a desiccant pump; and throttlingthe strong desiccant solution flowing from the heat exchanger by theexpansion valve and then feeding the strong desiccant solution into theabsorber.
 8. The method of claim 6, wherein the absorber is with coolingwater in and out so as to facilitate the absorption of the second watervapor into the strong desiccant solution and the dilution of the strongdesiccant solution, wherein the absorption of water vapor makes theabsorber maintained at a low pressure.
 9. The method of claim 6, whereinpressure inside the condenser is equal to pressure inside the desorber,and pressure inside the absorber is equal to pressure inside a space ofthe permeate side of the vacuum section.
 10. The method of claim 6,wherein at least one of the weak desiccant solution and the strongdesiccant solution comprises lithium bromide.
 11. An absorption vacuumdehumidification system, comprising: a vacuum section having a feed sideand a permeate side and comprising a hydrophilic membrane that separatesthe feed side than the permeate side; an absorber connected to thepermeate side of the vacuum section; a desorber connected to theabsorber to form a desiccant solution cycle path between the absorberand the desorber; a photovoltaic energy supply configured to power aheat source that provides hot liquid into the desorber; a heat exchangerconnected to the desiccant solution cycle path; a condenser connected tothe desorber; and a desiccant solution flowing along the desiccantsolution cycle path.
 12. The absorption vacuum dehumidification systemof claim 11, further comprising: a desiccant pump in communication withthe desiccant solution cycle path and configured to pump the desiccantsolution from the absorber to the desorber; and an expansion valve incommunication with the desiccant solution cycle path and configured tothrottle the desiccant solution from the desorber to the absorber. 13.The absorption vacuum dehumidification system of claim 11, furthercomprising: a vapor tube connecting the vacuum section to the absorbersuch that the hydrophilic membrane is physically free from the desiccantsolution cycle path at least by the vapor tube.
 14. The absorptionvacuum dehumidification system of claim 13, wherein the feed side isphysically separated from the desiccant solution cycle path at least bythe vapor tube and the permeate side.
 15. The absorption vacuumdehumidification system of claim 14, wherein the feed side of the vacuumsection is configured to provide a flowing path to allow moist airentering to flow through the feed side without involving with thedesiccant solution cycle path.